Thermal Properties of Small-Molecule Organic Semiconductors

Grants and Contracts Details


Intellectual Merit: In recent decades, there has been considerable interest in finding new electronic materials to replace conventional semiconductors in applications ranging from thin-film transistors to thermoelectrics. Because of the relative low-cost in their preparation and their flexible morphologies, there has been growing interest in using organic semiconductors, both polymers and crystals of small molecules. For new materials to be incorporated into electronic devices, especially nano-structures, it is important to know their thermal conductivities, so they can properly dissipate generated heat. There has also been growing interest in developing organic thermoelectric devices, for applications such as thermal energy harvesting in solar cells and heat-dissipation/energygeneration in uniforms. In addition to their low costs and flexible morphologies, layered organic materials have the advantage of typically low phonon thermal conductivities. We will be measuring the thermal conductivities and Seebeck coefficients of small molecule, crystalline organic materials developed at the University of Kentucky. The goal of this research will be both to screen new materials for thermoelectric applications and to gain understanding of how heat transport is correlated with structural properties. Measurements will be made both the interlayer and in-plane directions on bulk crystals and thin films, to assess how interfaces affect thermal properties. A variety of techniques will be used for thermal conductivity measurements, including a newly developed “ac” technique to measure the interlayer thermal conductivity. Since most techniques actually measure the ratio of the thermal conductivity and specific heat, the latter will be measured using differential scanning calorimetry. Thermopower measurements will be made on “co-crystallized” doped materials in which the dopant molecule substitutes for the host molecule without disrupting the crystal structure. Broader Impact: The P.I. has a long history of working with physics graduate students in experimental condensed matter physics research and preparing them for a variety of careers in academic and industrial research and teaching. Two graduate students will work throughout the academic year on this project (with possibly additional undergraduate and graduate physics students in summers), getting experience in a variety of techniques not only in characterization techniques, but in crystal and film growth, for which they will work closely with researchers in the University’s Chemistry Department. These students will also regularly attend (and give) departmental seminars and attend national and international meetings. In addition, the P.I. has considerable experience in working with undergraduate education majors, both in classes and in having them doing summer research in his lab. The goal of the latter program was to give students, especially those with career goals as elementary or middle-school teachers and who had no previous scientific research experience, the opportunity to get a hands-on taste of research that they could share with their future pupils. This program has been extremely successful and will be continued under the proposed program.
Effective start/end date7/1/136/30/18


  • National Science Foundation: $369,000.00


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